There are four in the series thus far. Great books if you want to read to your kids in Japanese - or for someone who wanted to start reading Japanese (all kanji has furigana).

Edit: See the link above for full details

Also forgot to mention that many of the story lines involve food in one form or another, hence the "Itadaki," in the title of the series - i.e. Japanese traditionally say "itadakimasu" いただきます before starting a meal. Great way to indoctrinate kids with Kinnikuman lore as well as good eating habits- lol